Injection site is hard as rock, help

I am injecting test for quite a long time now. I noticed that the last weeks the injection site in my buttocks is very hard and the needle gets very diffucult inside, i have to push really hard to get it inside the muscle. Why is this happening??? I use other injection sites aswell btw.

Was there any test prop in the injection? I get hard lumps for a week everytime I use Sustanon. Scar tissue can be broken up by rolling your glutes over a racket ball on the floor, hurts like hell but breaks up the scarring.